Process of adhering an organic coating to a polymeric substrate



Oct. 11, 1960 B. GRAHAM 5 PROCESS OF ADHERING AN ORGANIC COATING TO A POLYMERIC SUBSTRATE Filed June 5, 1956 SHAPED ORGANIC POLYMER, ED,

HYDRODARBDN, POLYESTER,

PDLYANIDE ETHER IRRAD IATE WITH LOH ENERGY PARTICLE RADIATION IN THE SUBSTANTIAL ABSENCE OF OXYGEN ACTIVATED SHAPED ORGANIC PDLYNER comer III'I-I DISSINILAR.

oncmc MATERIAL STA BLE DRAFT PDLYNER INVENTOR BDYNTDN DRAHAN BY M N.

ATTORNEY United States Patetit.

PROCESS OF ADHERING AN ORGANIC COAT- ING TO A POLYMERIC SUBSTRATE Boynton Graham, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware Filed June 5, 1956, Ser. No. 589,373

9 Claims. (Cl. 117-47) This invention is concerned with a new method of afiixing a coating of organic material to an organic polymer substrate.

It has been observed that coatings of organic materials can be afiixed to organic polymer substrates which'have been subjected to the action of high energy ionizing radiation. However, the exposure of synthetic polymers to highenergy radiation involves many side effects, including crosslinking and degradation, which alter the physical properties of the irradiated polymer.

It is an object of this invention to provide a process which utilizes relatively low energy radiation to cause organic coatings to be aflixed to organic polymer substrates without affecting the bulk physical properties of the substrate. Other objects of the invention will become apparent from the specification and claims.

There has now been discovered a process for aflixing to an organic polymer substrate a coating of a dissimilar organic material by subjecting the substrate in the substantial absence of oxygen to charged particle ionizing radiation having an energy of from 15 to 50,000 electron volts for a minimum exposure of 0.01 watt-seconds per square centimeter and thereafter, while the effect of irradiation is still active, coating the organic polymer substrate with a thin coating of the dissimilar organic material so that the coating is bonded to the substrate. This invention is shown broadly in the appended drawing, a

ried out may be varied from extremely low temperatures up to the decomposition temperature of the organic coating or substrate. The desired changes in the polymer substrate increase in stability as the temperature is lowered below room temperature and, for this reason, irradiation temperatures in the range of -70 to 0 C. are

preferred. However, there is little advantage in employ-- ing extremes of temperature when the efiect of the irradiation is adequate for thecoating conditions employed, and for reasons of convenience and economy, room temperature is then preferred.

In employing this invention, the organic polymer sub-' strate is first subjected to ionizing radiation having an energy of from 0.000015 to, 0.05. m'ev. and then subsequently, while the effect of irradiation is still active; contactecl with the dissimilar organic material which thereby the first 3-5 seconds of contact.

desirable. It has been observed, however, that the effects of the irradiation'can be sustained for longer periods of time, i.e., weeks and even months, particularly if the irradiated shaped polymer is kept in an inert atmosphere such as under nitrogen, argon, helium or the like and/or is stored at low temperature such as at 80 C. In general, the lower the temperature at which the irradiated shaped polmer is stored, the longer the time the surface remains active toward adhering a coating of a dissimilar organic compound. It is thus possible to irradiate the shaped polyer at a site of available radiation and then by maintaining suitable storage conditions as above to ship the irradiated polymer to another site for carrying out the contacting step. 7

The temperature at which the contacting step of this invention is carried out may be varied within wide Thus, the irradiated organic polymer may be contacted with the dissimilar organic compound at temperatures ranging from 70 to 300 C., depending on the thermal properties of the polymer and the coating material. A substantial portion of the aiiixing reaction occurs within The total duration of contact may be extensively prolonged if convenient, but excess of the dissimilar organic compound may be safely removed after 24 hours since no significant amount of material becomes afiixed after this time.

In carrying out the process of this invention it is essential that the irradiation-induced activity which leads to the bonding of the chemically dissimilar coating material to the polymeric substrate should not be unduly inhibited in forming nor substantially dissipated in side reactions other than bonding of the coating. This may be accom- I coating is large in comparison with the enclosure in which the irradiation is efiected or when the exposure to oxygen is very brief, but the amount of oxygen should not be sufificient to react with all the radiation-induced active centers-formed. Operating in a vacuum, or at least under reduced pressure, is frequently desirable since this not only serves to reduce the concentration of oxygen but lowers the number of collisions of the radiation particles with other gases that might be present, and thereby increases the efiiciency of the irradiation.

Under some circumstances, the efliciency of irradiation is increased when the surfacebeing irradiated is electrically grounded. This is accomplished by selecting a polymer substrate which is at least somewhat electrically conductive and grounding the substrate.

By organic polymer substrate we mean any natural or synthetic normally solid organic polymeric material,

particularly those with molecular Weights in excess of r 500. The polymer may be oriented or unoriented. Thus, f there may be employed hydrocarbon polymers, such as becomes permanently attaehed'to the substrate. The time which may elapse between the irradiation step the contacting step will vary with the radiation exposure,

- temperature and atmosphere of storage, and the chemical nature of the irradiated polymen, A storage time of not a time of less than one second between steps is frequently polyethylene, polystyrene, polybutadiene, rubber, polyisobutylene, butadiene/styrene copolymers and the like; halogenated hydrocarbon polymers, such as polyvinyl chloride, polyvinylidene chloride, polychloroprene, polytetrafluoro'ethylene, polyvinyl fluoride, chlorinated and chlorosulfonated polyethylene and the like; ester-containing polymers, such as polyvinyl acetate, polymethyl methacrylate, polyethylene terephthalate and the like; hy- "droxyl-containin'g polymers, such as polyvinyl alcohol, cellulose, regenerated cellulose and the like; ether-containingjpolymers, such as polyethylene oxide, polymeric ;;formaldehyde, solid polytetrahydrofuran, dioxolane pjolyiners and the like;-condensation polymers, such asnylons,

polyimides, phenol-iormaldehyde polymers, urea-formaldehyde polymers,triazine-formaldehyde polymers and the lilre, polypeptides, silicones, olefin polysulfones as well as natural polymers such-as wool, cotton, silk and the like. The chernical nature of the organic matrialfused to form coatingsin accordancewiththis inventionis'limited only by the requirement that it be chemicallydistinguishable. from the substrate." Thus, the invention comprises adhering a layer of organic material which is che'mi-' caly dissimilar *to the polymeric substrate. 'The organic coating material may be irithe form of'a gas .or vapor which is brought in contact with the irradiated sub strate. Liquids maybeapplied tothe substrate by any of theusual methods of coating, such as .by dipping, I

spraying, brushing, printing and the like; So lids may be appliedto the substrate. by sublimation or by coating.

from melt. Theiorganic compound which comprises the coating may be a hydrocarbon, halogenated hydrocarbon;

alcohol, amine, aldehyde, k etone', ether, acid,,ster, amide, 'phenol, sulfonic acid, nit'ro compound, tat, protein, syntheticpolymer and other organic-compounds which contain at least one 'C/X bond, where X is hydrogen or halogen. It is preferablethat the organic compound be 1 a material which is normally incompatible with thesubstrate and has 'no solvent action thereon.

Among the non-polymeric organic 'compounds a' pre-- -ferred group of coating materials which are highly reactive in the process ofthis invention are the chain transfer agents, e.g., compounds containing active hydrogen or halogen such aschloroform, carbon tetrachloride,

p nylmethane, thiols, secondary alcohols, maleic anhydride and the like. '1

Another preferred group of non-polymeric foiganic coating compounds are those which are normally nonpolymerizable, since with them the amount of coating *fatfixed by the process of. this invention is most readily controlled. n r r organic compoundsgare The low energy ionizing charged particlejradiation employed the present invention may be'in such forms as alpha particles 'or electrons and is limited only. by the energy it possesses atthe time it reaches the substrate to which the;coating is to be aflixed. The lowenergy charged particle radiation maybe generatedby known methods that dofnot form a part of this invention Thus, particles of suitable energy may be obtained by means'of appropriate voltage gradients; using such devicesas: a cathode raytube, a resonant'cavity accelerator, a; Van de Graafi generatorior the like. Theaccele'r T i ated; particles maybe utilized in a vacuum by introducing the" substrate into thevacuum chamber of the accelerator.. A1t ernatively, the. accelerated electrons or alpharparticles may be let out in known manner-through a window and r utilized in-air or'a gas ,'with'due precautions being taken that the particles have the. desired energy when rthey impingeon ther substrate." A preferredradiationin the process of this inventionisjthat obtained from l dw renergyr'electronslwhich are readily generated by means of a suitable voltage gradient, such as thatsnpplied by an induction coil of. the Tesla' type This form'rof radiation is preferred because r of its ready availability, ldw

f costar dflsharply defined penetration n 'lfhe invention will be-better pnderstood reference 6 to, the example,which illustrates ,a specific. embodiment" a ,of theprocessa oated0.0015 inch thicl; cellophane (m ram PTf cellophane) is irradiated in a demountable cathodeiray'tube withoZS kev. elegtrons at 10microamps this invention.

maining in the monomer in the dark at room temperature under nitrogen for hours, the film is removed and air-dried. The side of the film which had been exposed to the electron beam is found to have become 5 more resistant to wetting by liquid water, andrto have acquired a 0l0006inch coating of polyvinylidene chloride which is not removed byifextrjacting 'for 3 days with dioxane .in arsoxhlet apparatus. In contrast, the side of the film which had not been exposed to thevelectron beam 10 does not exhibitimproved resistance to Wetting by'liquid water; and hasnotacquired acoating oi polyvinylidene chloride f1 1 r In a similar manner other"organic' materials may be affixed'toorganic ,polymer substrates bythe process of v For example, polyethylene film after irradiation with felectronsi'or alphaparticles of suitable energy may be contacted with glycerol or. polyethylene glycol to aih x hydrophilic'coatings to the surface of the V polythylene. Irradiated nylon fabricmay be contacted 20 with palmitiq acid to afiix' a hydrophobic coating of the latter to the nylon. In this invention charged particles fwith energy inthe range-$10,000 to 50,000- electron iVOltS represent azpreferred fornr oi radiation. .-Ari..important advantage of the present invention is .that' coatings of non-polymerizable as well as polymerizahle materials are aflixed by the utilization of low-cost radiation energy with an attendant minimum radiation 7 hazard. Another important advantage is that by limiting the energyof radiation employed, excessive crosslinking,

degradation and otherchanges inthe physical properties ofthe organic polymer substrate are avoided. s g r The process of this invention is particularly useful .for a permanently aflixingsizes to fibrous organic polymeric materials; finishing agents, anti-static coatings, and coloring materials'jto'fabrics; and fslip agents, waterproofing layers, etc., to films such as cellophane. f

v Since many different embodiments of the invention may be made without departing from the spiritand scope ithcreof it is to be-unders'tood that the invention is not limited by'the specific illustrations except to the extent defined in thefollowingclaims; in a What-is claimed is? f 7 1. In a process torcoating "an organic polymer substrate with a dissimilar organic material, the improvemento f subjectingthepolymerfsubstrate inth'e substantial absence 7 of oxygen tOQioniZing charged particle radiation having anenergyofifromfIS to 150,000 electron volts for a' minimum exposure of 0.01 watt seconds per square 1 centimeter but ioramaximum exposure tinsufficient to dead an p s nis xms and th e whilethe effect 7 of irradiation. is stillgactiyeqapplying a coating of the dissimilar organic materialtolthe organic polymer. .2 A.p q s asdefinsd nisl m whe e the i- 1 sdpp m sat iwi h. a d im ;n -n ym rjiizable organic compound; 1

j 3.; A process as defined. in claim '1 wherein the iriradiate'd polymer is. coated with a jdissimilar organic polymer. 'I Q r ,7 0;, .4. A processl as defined in claim l wherein theirradiated polymer, is coated with.aa'dissirjrnlar polymeric ethen. T

.1} 5. ,Agprocess defined ;in claim '1, whereinthe time elapsing between 'subjectingthef organic, polymer sub- 5 strate to -ionizing radiation and applying the coating of a dissimilar .organic. material theretoiis "not. longer than V poly mer substrate is cellophane.

7 7; The;process of claim 6 in which the o r aganicjrnateriali is p'olyyinylidene' chloride. r p

'8'. Aproc'esslasdefined in claim l'wherein the ionizing charged particleradiation is ia memberof the groupconsisting oflel ectroris nd alpha particles-L phane shape in the substantial absence of oxygen with electrons having an energy of 15-50,000 electron volts for a minimum exposure of 0.01 watt-second per square centimeter but for a maximum exposure insufiicient to degrade the cellophane and thereafter while the effect of irradiation is still active contacting the cellophane with vinylidene chloride and thereby bonding polyvinylidene chloride to the cellophane.

References Cited in the file of this patent UNITED STATES PATENTS 2,666,025 Nozaki Jan. 12, 1954 2,766,220 Kantor Oct. 9, 1956 FOREIGN PATENTS 1,079,401 France Nov. 30, 1954 1,079,401 France Dec. 12, 1955 (4th Addition No. 66034) 6 OTHER REFERENCES Modem Plastics, volume 32, N0. 10, June 1955, pages 159, 252 and 254.

B.N.L. 367, pages 27, 28. Quarterly Progress Report, July 1-Sept. 30, 1955. February 1956.

B.N.L. 375, page 26. Quarterly Progress Report, Oct. l-Dec. 31, 1955. April 1956.

I and E Chem, vol. 45, pages 11A and 13A, September 1953.

Nature, vol. 170, pages 1075, 1076; Dec. 20, 1952.

Sun: Modern Plastics, vol. 32, pages 141-144, 146. 148, 150, 229-233, 236-238. 

1. IN A PROCESS FOR COATING AN ORGANIC POLYMER SUBSTRATE WITH A DISSIMILAR ORGANIC MATERIAL, THE IMPROVEMENT OF SUBJECTING THE POLYMER SUBSTRATE IN THE SUBSTANTIAL ABSENCE OF OXYGEN TO IONIZING CHARGED PARTICLE RADIATION HAVING AN ENERGY OF FROM 1K TO 50,000 ELECTRON VOLTS FOR A MINIMUM EXPOSURE OF 0.01 WATT-SECONDS PER SQUARE CENTIMETER BUT FOR A MAXIMUM EXPOSURE INSUFFICIENT TO DEGRADE SAID ORGANIC POLYMER AND THEREAFTER WHILE THE EFFECT OF IRRADIATION IS STILL ACTIVE APLYING A COATING OF THE DISSIMILAR ORGANIC MATERIAL TO THE ORGANIC POLYMER. 